29 July 2009

Energy produced from empty mines

Mine shafts about to shut down do not have to be a burden; they may be able to provide geothermal energy to towns.

A new method makes it possible to estimate the amount of heat a tunnel could potentially provide, said Rafael Rodríguez, from the University of Oviedo’s Higher Technical School of Mining Engineering in Spain.

“One way of making use of low-intensity geothermal energy is to convert mine shafts into geothermal boilers, which could provide heating and hot water for people living nearby,” Rafael Rodríguez. This type of energy comes from the internal heat of the Earth.

Rodríguez and his colleague María Belarmina Díaz developed a “semi-empirical” method (part mathematical and part experimental) to calculate the amount of heat a mine tunnel that is due to be abandoned could produce. They base their method on studies carried out while the mine is still in use.

“When the mine is still active, one can access the tunnels easily in order to gather data about ventilation and the properties of the rocks, as well as to take samples and design better circuits, and even program the closure of some sections in order to use them for geothermal energy production,” said Rodríguez, who added you can produce geothermal energy, but once the mine closes, “it is no longer possible by that stage to make any modifications, or to gather any useful data to evaluate and improve the system.”

The study looks into geothermal exploitation of a 2-kilometer-long mine shaft, in which the temperature of the rocks 500 meters below the surface is around 30ºC. This is typical of many of the mining areas in Asturias, Spain, although it could also apply to other parts of the world. As a part of the process, they could force water in through tubes at 7ºC and return at 12ºC, a big enough heat gain to be of benefit to towns located above the mines.

Aside from their predictable energy production levels, the geothermal boilers in mine shafts also function practically as an open tube system “but without any risk of heat contamination of aquifers,” Rodríguez said.

Using geothermal energy also helps to reduce carbon dioxide emissions and is not dependent upon climatic conditions (unlike other renewable energies such as solar or wind power). Other advantages are these facilities make use of a country’s own resources, do not require new developments on large sites, do not pollute the immediate environment, and should be profitable over the long term.

For related information, go to www.isa.org/manufacturing_automation.